We will further study the regulation of genetic activity in the hemoglobin model system in the following circumstances; 1) The switch from gamma to beta chain production in late fetal development will be studied by assaying globin mRNA concentrations and 5' capping, an mRNA processing step. 2) The means for balanced globin synthesis in erythroid development in the mouse spleen and in reticulocytes of other species will be studied at the mRNA. 3) Abnormal regulation of globin synthesis in the beta-thalassemia syndromes will be attacked by determining rates of globin mRNA transcription and processing in individuals with these mutations. BIBLIOGRAPHIC REFERENCES: Cheng, T-c. and Kazazian, H.H., Jr.: Unequal accumulation of alpha- and beta-globin mRNA in erythropoietic mouse spleen. Proc. Nat. Acad. Sci. USA 73:1811-1815, l976. Kazazian, H.H., Jr., Silverstein, A.M., Snyder, P.G., and Van Beneden, R.J.: Increasing haemoglobin beta-chain synthesis in foetal development is associated with a declining gamma- to alpha-mRNA ratio. Nature 260:67-70, l976.